A banned neonicotinoid insecticide known as ‘clothianidin’ impairs honey bees’ ability to learn, but has no adverse effects on bumblebees.
By Lola Gayle, Editor-at-large
Not all bees are equal when it comes to how pesticides and parasites affect their colonies. In fact, new research shows that honey bees suffer significant learning defects when exposed to a pesticide that was banned by the European Union in 2013. However, bumblebees seem to be immune to the effects.
The banned pesticide is a neonicotinoid insecticide known as ‘clothianidin‘. Neonicotinoids are a class of insecticides that are chemically similar to nicotine, which has been used as a pesticide since the late 1700s. Clothianidin and other neonicotinoids act on the central nervous system of insects as an agonist of acetylcholine.
Note:An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Whereas an agonist causes an action, an antagonist blocks the action of the agonist and an inverse agonist causes an action opposite to that of the agonist.
For the new study, scientists from the University of Sussex exposed honey bee and bumblebee workers to the pesticide for 11-12 days. They then assessed the effect of the pesticide using a proboscis extension reflex conditioning assay, which tests how bees learn to associate an odor with a sugar reward.
The scientists found that clothianidin impaired the honey bees’ ability to learn the association, but surprisingly had no adverse effects on the bumblebees.
According to a statement from the researchers, the findings come after the European Food Safety Authority announced earlier this year it is to review the moratorium on use of three pesticides, including clothianidin, and will report back by the end of January 2017.
“Our research has important implications for global regulatory assessments which generally use honeybees as a model for all bees,” said Dave Goulson, Professor of Biology at the University of Sussex. “We show for the first time how this banned pesticide, while having a significant negative effect on learning in honeybees, had no adverse effects on learning in bumblebees. This is unexpected, since previous work suggested that this pesticide has a more pronounced impact on colonies of bumblebees than on those of honeybees.
“During a time when the EU regulation of certain pesticides is being reviewed,” Goulson continued, “we must ensure regulators learn from this research and do not readily extrapolate findings from one bee species to others.”
The researchers also looked at how the microsporidian parasite Nosema ceranae, which is a potential major threat to honey bee populations in Europe, affects the memory and learning of both species. The study found that infection by the parasite slightly impaired learning in honey bees, however the parasite did not infect bumblebees.